The present invention relates to the hydrometallurgical processing of nickeliferous or cobaltiferous ores and, in particular, to the direct recovery of nickel and cobalt from a laterite leach slurry by extraction with ion exchange resin, which is then physically separated from the leach slurry.
A number of new processes are being developed for the extraction of nickel and cobalt from nickeliferous oxide and laterite ores. Each of these processes dissolve the metal values with mineral acid, followed by solid/liquid separation and neutralization before final metal recovery. The selective metal recovery from the leach slurry is an important step in the design of an economical process. The solid/liquid separation due to the fine particle size distribution and behavior of the leach slurry as well as the selective metal separation from the impurities add cost and complexity to this process.
Nickeliferous oxide ores are formed by weathering of nickel-bearing olivine-rich ultramafic bedrock. The dissolution and re-deposition of the metals produces a very fine material, typically having a particle size less than 50 xcexcm. These materials can contain substantial amounts of smectite clay. The fineness and behavior of this material rules out filtration as a method of solids/liquid separation, which is normally required for metals recovery from the pregnant leach solution. The other separation method of settling is most effectively accomplished by gravity separation of the fine laterite leach residues in a series of thickeners. To minimize the entrained metal losses, continuous counter-current decantation (CCD) in a series of at least six thickeners is used for solid/liquid separation. To allow proper settling of the solids and to produce a clear overflow for metals recovery, large thickeners (over 50 meters in diameter) are required for each stage. The thickener unit area for each unit for nickel acid leach residues is around 0.1 m2/(t/d). This compares unfavorably with a unit thickening area requirement of around 1 m2/(t/d) for settling mineral slurry solids. The large area required for settling of laterite leach slurries, not only affects the overall size of the plant, but also bears a cost. The capital cost for the CCD circuit can be up to 30% of the capital cost of the titanium-clad autoclave in the pressure leaching circuit. These costs are for conventional thickeners, in which fresh water is used. Because some of the laterite deposits are located in arid areas, the available water is saline. In this case, the presence of chlorides in the water requires more expensive materials of construction, because stainless steel at elevated temperatures is not adequately resistant to chloride ions. Therefore, a further significant increase in the capital costs for this thickener area is required when saline water has to be used.
In addition to the capital cost, the operating cost not only includes power consumption for each rake mechanism, but also includes flocculant used for settling the fine material. The flocculant consumption ranges from about 200 to over 800 grams per tonne of solids, which adds up to 10% to the total plant operating costs.
Nickel and cobalt recovery from the clear pregnant leach solution can be done in various ways, but is complicated by the presence of many impurities, such as copper, iron, and manganese. One method to selective extract only nickel and cobalt is by ion exchange, as described in U.S. patent application Ser. No. 08/796,297. Although this patent describes a method to selectively recover nickel and cobalt, it is based on processing of clear leach liquor. In other words, this method requires a solid/liquid separation unit operation after leaching and prior to metals recovery.
In a different metallurgical application, the direct recovery of gold from slurry or pulp by the use of resin-in-pulp (RIP) was developed as an improvement on the carbon-in-pulp process (CIP). The carbon-in-pulp process was developed in the U.S.A. and South Africa during the 1970s (see P.A. Laxen, xe2x80x9cCarbon-in-pulp processes in South Africaxe2x80x9d, Hydrometallurgy, Vol. 13,1984, pp.169-192). Replacing carbon with ion exchange resin is advantageous, because (i) resins offer higher loading capacity and loading rate, (ii) can be more abrasion resistant and (iii) are less likely to be poisoned by organic matter.
The first commercial resin-in-pulp gold extraction plant was the Golden Jubilee Mine in South Africa (see C. A. Fleming, xe2x80x9cRecovery of gold by Resin-in-pulp at the Golden Jubilee minexe2x80x9d, Precious Metals ""89, Edited by M. C. Jha and S. D. Hill, TMS, Warrendale, Pa., 1988, pp. 105-119). Based on the industrial operation at the Golden Jubilee Mine, Fleming analyzed the advantages of RIP versus CIP (C. A. Fleming, xe2x80x9cResin-in-pulp as an alternative process for gold recovery from cyanide leach slurriesxe2x80x9d, Proceedings of 23rd Canadian Mineral Processors Conference, Ottawa, January 1991).
As another metallurgical application of the use of resin for metal recovery from slurry, Slobtsov reports that the RIP process can be used to recover additional copper from oxide and mixed ores after conventional flotation for primary copper extraction. In this proposed process, the copper recovery would increase by 7 to 9% by the addition of a resin-in-pulp step after flotation (L. E. Slobtsov, xe2x80x9cResin-in-pulp process applied to copper hydrometallurgyxe2x80x9d, Copper ""91, Volume III, pp. 149-154). A resin with aminodiacetic functionality was used to absorb copper, using either sulfuric acid or ammonia-ammonium carbonate solution as the stripping solution. In this application, the resin-in-pulp process is a secondary recovery step to improve the overall copper recovery.
Johns and Mehmet (M. W. Johns and A. Mehmet, xe2x80x9cA resin-in-leach process for the extraction of manganese from an oxidexe2x80x9d, Proceedings of MINTEK 50: International Conference on Mineral Science and Technology, Published by Council for Mineral Technology, Randburg, South Africa, 1985, pp. 637-645) described the resin-in-leach process, with specific application to extraction of manganese from an oxide. Part of the discussion focused on the compromise of leaching and resin loading with respect to acidity of the solution.
All of the above processes and proposed applications benefit from the direct metals recovery from leach slurry. In these applications, however, solid/liquid separation is simple and conventional and the metal extraction from leach liquor is comparably straight-forward. Therefore, these processes don""t offer any substantial improvement over existing processes.
In the gold industry, one advantage for replacing carbon with resin is the increased abrasion resistance of ion exchange resins, which lowers the operating cost related to this consumable. In the laterite leach slurry, it is postulated that the presence of clay reduces the abrasion of the resin. The rheology of the laterite leach slurry is such that solid ore particles are suspended in a fluid medium consisting of ultrafine clay particles and water. As a result, the resin is also suspended within the slurry. This phenomenon significantly reduces resin degradation due to mechanical abrasion.
In the proposed process, a relatively coarse ion exchange resin is added directly to the leach slurry, which contains ore particles much smaller than the ion exchange resin beads. The desired metal(s) are extracted onto the resin and then the resin is separated from the depleted leach slurry by screening or other suitable techniques. Therefore, the present invention provides a novel method for direct metal recovery from acid laterite leach slurry, by elimination of the costly CCD circuit and selective extraction of nickel and cobalt from laterite ores.
The present invention provides a process for the direct recovery of nickel and cobalt from nickeliferous and/or cobaltiferous oxide ore leach slurry by ion exchange. In one embodiment of the present invention, a nickeliferous ore is leached with mineral acid to solubilize the metals and to form a pregnant solution and leach residue slurry. The nickeliferous ore is selected from the group consisting of laterite ore, oxide ore, and mixtures thereof. The nickeliferous ore contains a first metal selected from the group consisting of nickel, cobalt, or mixtures thereof together with a second metal selected from the group consisting of copper, iron, chromium, magnesium, manganese, aluminum, calcium, and mixtures thereof. The resulting pregnant leach slurry is contacted with ion exchange resin, which selectively loads the nickel and cobalt from the pulp. Preferably, the ion exchange resin is added to the slurry. During the contact of the ion exchange resin with the slurry, the pH may be adjusted by the addition of a neutralizing agent. This is a major advantage of the present invention because pH control in-situ during the ion exchange extraction process allows optimization of metal extraction, which is pH dependent. In another embodiment, the pregnant leach slurry is partially neutralized prior to contacting with the ion exchange resin.
The resin is separated from the leach residue slurry by screening. The metals may be eluted with an acidic or an ammoniacal solution. Multiple contact and screening steps may be employed to effect counter-current flow of leach slurry and resin, thereby improving extraction efficiency. Preferably, the eluting solution is a dilute, acidic solution. After eluting, the resin is returned to the loading cycle. The metal-depleted slurry proceeds to disposal. This process eliminates the difficult and cost intensive solid/liquid separation, which would otherwise be required to recover metals values from the pregnant leach slurry.
It is to be noted that, unless otherwise stated, all percentages stated in this specification and appended claims refer to percentages by weight.
These and other objects, advantages, and features of the present invention will be better understood upon review of the following detailed description.